For the micro-fabrication of semiconductor integrated circuits, radiant rays having a shorter wavelength are required for an exposure (lithography). Light source devices which emit light having a wavelength of 11 to 14 nm called extreme ultraviolet radiation (hereinafter referred to as EUV radiation) are being developed. Among methods of generating the EUV radiation, there is a method of generating high temperature and high density plasma by discharge so as to emit EUV radiation. As an example of an apparatus to which the method is applied, there is an apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2003-218025.
FIG. 7 shows a schematic view of an extreme ultraviolet radiation generator (hereinafter referred to as EUV radiation generator) which emits EUV radiation from plasma.
A ring-shaped first main electrode 11 (breakdown voltage impression electrode: cathode), and a second main electrode 12 (ground electrode: anode) are disposed so as to hold an insulator 13 therebetween. In a high temperature and high density plasma generating space 10, plasma is generated. The diameters of holes of the rings are about φ5 to 20 mm.
A chamber 14 which is a discharge container, is divided into a first container 14a on the side of the cathode, and a second container 14b on the side of the anode, which are separated and insulated by the insulator 13. For example, an Xenon (Xe) gas which is discharge gas, is introduced from an gas inlet 14c of the first container 14a to which a gas supply unit 20 is connected, and is discharged into a gas discharge unit (not shown) connected to the second container 14b from a gas outlet 14d. 
The pressure of the high temperature and high density plasma generating space 10 is adjusted to 1 to 20 Pa by a vacuum pump connected to the second container 14b. 
As described above, the second main electrode (anode) 12 is grounded, and a breakdown voltage of about −5 kV to −20 kV is applied to the first main electrode (cathode) 11 from a high voltage pulse generating unit 21. If the discharge gas, such as Xenon (Xe), is allowed to flow between the two electrodes, high temperature and high density plasma discharge is caused at 1 to 10 kHz inside the rings of the electrodes 11 and 12, and EUV radiation having a wavelength of 13.5 nm is emitted from the plasma. The emitted EUV radiation is led to a radiation-emitting portion 16 by collector optics unit 15 (EUV collector optics) provided in the second container 14b. 
The reason why the second main electrode (anode) 12 is grounded is to prevent electric discharge from occurring between optical components of the collector optics system 15 (EUV collector optics) provided adjacent to the second main electrode 12. The optical components are attached to a chamber container and are at the ground potential along with the container.